Science News

A drug already approved for treating type 2 diabetes may have neuroprotective effects that could help people with Parkinson’s disease (PD), according to research published in the May 20 online issue of the Journal of Clinical Investigation. This first, small clinical trial testing the drug exenatide (Byetta®) in people with PD, points to a potential treatment for PD. It also demonstrates a way to inexpensively determine whether existing therapies for other diseases should be investigated further in PD.

Researchers led by Thomas Foltynie, M.B.B.S., Ph.D., at University College London, United Kingdom, knew that studies of exenatide in animal models of PD showed that it had potential beyond treating diabetes. The drug also improved learning and memory and had neuroprotective effects, meaning it could protect brain cells. It was already being tested for use in Alzheimer's. In addition, since exenatide was already approved for treating diabetes, they also knew that it was proven to be safe.

Dr. Foltynie and colleagues questioned how to test the drug's potential in Parkinson's using the gold-standard “double-blinded” clinical trial – in which neither medical personnel nor volunteers should know who receives the treatment being tested and who receives placebo. This is because exenatide is injected with a special pen, which is expensive and logistically difficult to replicate as a placebo. So the researchers designed a single-blind trial: all of the 44 study participants received standard medical care for their moderate-stage PD, and 20 of them also took exenatide for 12 months. Physicians, not knowing who received the drug or not (they were “blinded”), evaluated participants’ PD symptoms at the beginning of the study, and after six, 12 and 14 months.

Results

Participants who took exenatide tolerated the drug well, although weight loss was a common side effect.

After 12 months, participants who took exenatide showed a modest improvement in PD symptoms when off medication; those not receiving the drug declined slightly compared to their scores at the beginning of the study.

Participants in the exenatide group also showed modest improvements in measurements of cognition compared to the start of the study, while the control group declined slightly at 12 months.

At 14 months, two months after exenatide treatment stopped, participants who had taken it showed improvement while those in the control group saw a decline in their symptoms. Measurements of cognitive symptoms did not change from the 12 month values.

What Does It Mean?

The results of this initial study of exenatide, an anti-diabetic drug, for use in Parkinson's, are encouraging. However, the number of participants in this trial was small (21 in the group treated with the drug), and it is possible that improvements in the group taking exenatide can be attributed to the placebo effect (as participants knew if they were taking the drug). The fact that the benefits lasted after exenatide treatment ended, however, could also suggest that the drug may indeed slow disease progression.

The study authors conclude that exenatide appears to be safe to use and should be considered for testing in a large double-blind, placebo-controlled trials to assess its potential for PD.

Clinical trials are very expensive and take a very long time. This study demonstrated a way of helping to identify a therapy for PD in a relatively cheap way – by using an already approved drug, on a small sample of participants who knew whether they were taking the drug or not. If the drug proves itself effective in a larger trial, this will confirm the cost-effectiveness of their methods.